1. Field of the Invention
The present invention relates to a liquid discharge head for recording an image on a recording medium by discharging a liquid droplet such as an ink droplet and a method for manufacturing such a head, and more particularly, it relates to a liquid discharge head for performing ink jet recording.
2. Related Background Art
An ink jet recording system is one of so-called non-impact recording systems.
In the ink jet recording system, noise generated during the recording is very small which is negligible and high speed recording can be achieved. Further, the ink jet recording system has advantages that the recording can be performed on various recording media so that ink can be fixed with respect to even a so-called normal or plain paper without requiring special treatment and that a highly fine image can be obtained with a low cost. Due to such advantages, the ink jet recording system has recently been used widely not only as a peripheral device of a computer but also as recording means for a copier, a facsimile, a word processor and the like.
As ink discharging methods of the ink jet recording system generally used, there are a method in which an electrical/thermal converting element such as a heater is used as a discharge energy generating element used for discharging an ink droplet and a method in which a piezoelectric element is used, and, in both methods, the discharging of the ink droplet can be controlled by an electric signal. A principle of the ink discharging method using the electrical/thermal converting element is that, by applying voltage to the electrical/thermal converting element, the ink in the vicinity of the electrical/thermal converting element is boiled instantaneously so that the ink droplet is discharged at a high speed by rapid growth of a bubble caused by phase change of the ink during the boiling. On the other hand, a principle of the ink discharging method using the piezoelectric element is that, by applying voltage to the piezoelectric element, the piezoelectric element is displaced to generate pressure by which the ink droplet is discharged.
The ink discharging method using the electrical/thermal converting element has advantages that a great space for containing the discharge energy generating element is not required and that a structure of the liquid discharge head is simple and nozzles can easily be laminated. On the other hand, inherent disadvantages of this ink discharging method are that a volume of the flying ink droplet is changed when heat generated by the electrical/thermal converting element is accumulated in the liquid discharge head and that cavitation caused by extraction of the bubble affects a bad influence upon the electrical/thermal converting element and that, since air dissolved in the ink remains as residual bubbles, a bad influence is affected upon an ink droplet discharging property and image quality.
In order to eliminate such disadvantages, ink jet recording methods and liquid discharge heads have been proposed, as disclosed in Japanese Patent Application Laid-Open Nos. 54-161935, 61-185455, 61-249768 and 4-10941. That is to say, the ink jet recording methods disclosed in such patent documents are designed so that the bubble generated by driving the electrical/thermal converting element in response to a recording signal is communicated with atmosphere. By using such ink jet recording methods, the volume of the flying ink droplet is stabilized so that a very small amount of ink droplet can be discharged at a high speed and endurance of the heater can be enhanced by eliminating the cavitation generated by extraction of the bubble, thereby obtaining a further finer image easily. In the above-mentioned documents, as an arrangement in which the bubble is communicated with the atmosphere, an arrangement in which a minimum distance between the electrical/thermal converting element and the discharge port is made to be considerably smaller than the minimum distance in the prior art is described.
Now, such a conventional liquid discharge head will be explained. The conventional liquid discharge head includes an element substrate on which electrical/thermal converting elements for discharging the ink and an orifice substrate joined to the element substrate and constituting ink flow paths. The orifice substrate is provided with a plurality of discharge ports for discharging an ink droplet, a plurality of nozzles through which the ink flows and a supply chamber for supplying the ink to the respective nozzles. Each nozzle includes a bubbling chamber in which a bubble is generated in the ink by the corresponding electrical/thermal converting element and a supply path for supplying the ink to the bubbling chamber. The element substrate is provided with the electrical/thermal converting elements disposed within the respective bubbling chambers. Further, the element substrate is provided with a supply port for supplying the ink to the supply chamber from a back side of a main surface of the element substrate contacted with the orifice substrate. The orifice substrate is provided with discharge ports opposed to the corresponding electrical/thermal converting elements on the element substrate.
In the conventional liquid discharge head having the above-mentioned construction, the ink supplied from the supply port to the supply chamber is supplied through the nozzles to fill the bubbling chambers. The ink supplied to each bubbling chamber is flown toward a direction substantially perpendicular to the main surface of the element substrate by a bubble generated by film boiling caused by the electrical/thermal converting element and is discharged from the discharge port as an ink droplet.
In a recording apparatus having the above-mentioned liquid discharge head, it is devised that a recording speed is made faster in order to obtain higher image quality output of a recorded image and a high quality image and high resolving power output. Regarding the conventional recording apparatus, U.S. Pat. Nos. 4,882,595 and 6,158,843 suggest a technique in which the discharging number of ink droplets flying from each nozzle of the liquid discharge head is increased, i.e. discharging frequency is increased in order to increase the recording speed.
Particularly, in U.S. Pat. No. 6,158,843, there is proposed an arrangement in which a flow of the ink from the supply port to the supply path is improved by providing a restriction space or a fluid resistance element which restricts the passage for the ink locally in the vicinity of the supply port.
Further, Japanese Patent Application Laid-Open No. 2000-255072 discloses a manufacturing method in which a single soluble resin layer is used on an element substrate so that, when the organic resin layer is exposed and developed, by using a photo-mask having a pattern smaller than a limited resolving power, a partially recessed portion is formed in each supply path. However, an upper surface of the flow path pattern formed by this method includes minute unevenness by the influence of scattering of exposing light.
By the way, in the above-mentioned conventional liquid discharge head, when the ink droplet is discharged, a part of the ink filled in each bubbling chamber is pushed back toward the supply path by the bubble growing in the bubbling chamber. Thus, there is inconvenience that the discharging amount of the ink droplet is decreased by reduction in volume of the ink in the bubbling chamber.
Further, in the conventional liquid discharge head, when the part of the ink filled in the bubbling chamber is pushed back toward the supply path, a part of pressure of the growing bubble facing to the supply port is escaped toward the supply path or is lost by friction between inner walls of the bubbling chamber and the bubble. Thus, the conventional liquid discharge head has a problem that the discharging speed of the ink droplet is decreased by reduction pressure of the bubble.
Further, the conventional liquid discharge head also has a problem that, since the volume of the small amount of ink filled in the bubbling chamber is changed by the bubble growing in the bubbling chamber, the discharging amount of the ink is dispersed.